FSH Format

EA PC SHAPE FORMAT - By Darkmatter and Karybdis

FSH SHPI Header

SHPI (4 bytes)

INT32 - File Size

INT32 - Number of Entries

Directory ID (4 bytes)

Directory ID legal entries:

G354 - Building Textures

G264 - Network Textures, Sim Textures, Sim heads, Sim animations, Trees, props, Base textures, Misc colours

G266 - 3d Animation textures (e.g. the green rotating diamond in loteditor.dat)

G290 - Dispatch marker textures

G315 - Small Sim texture, Network Transport Model Textures (trains etc)

GIMX - UI Editor textures

G344 - BAT gen texture maps

FSH Directory

Entry Name (4 bytes)

INT32 - Offset of the entry in the file

Entry names:

!pal - Global palette for 8-bit Indexed Bitmaps.

0000 - Buildings, props, network intersections,and terrain textures.

rail - Always used for a rail texture, whereas for street road intersections its always by instance.

TB2 - First sprite animation entry in a directory.

TB3 - Any sprite animation entries in a directory after TB2.

FSH Entry Header

BYTE - Record ID (logically anded by 0x7f for bitmap code or 0x80 to check if the entry is QFS compressed (unused by SC4))

INT24 - Size of the block including this header, only used if the file contains an attachment it is zero otherwise. For single images this is usually: width x height + 10h(hex). For images with embedded mipmaps, this is the total size of the original image, plus all mipmaps, plus the header. In either case, it may include additional data as a binary attachment with unknown format.

UINT16 - Width

UINT16 - Height

UINT16 - X axis coordinate for center of image or for image to spin around. 65535 Max.

UINT16 - Y axis coordinate for center of image or for image to spin around. 65535 Max.

UINT16 - X axis position to display the image from the left. Larger values offset image to the right. 4095 Max. (12 bits, 4 MSB (most significant bits) are always 0)

UINT16 - Y axis position to display the image from the top. Larger values offset image down the screen. 4095 Max. (12 bits, 4 MSB specify number of embedded mipmaps)

The center coordinates and offsets do not seem to be used by Sim City 4, but the nibble specifying embedded mipmaps is useful.

Bitmap or palette data

After the entry header is the bitmap or palette pixel or color information. Palettes are generally arrays of 1 byte each, 256 entries long. Bitmaps may store their pixel data in one of many ways. FSH images can store their pixel data raw, or they can make use of Microsoft DXTC compressed formats.

Bitmap codes:

0x7B - 8-bit indexed Palette: directly follows bitmap or uses global palette Compression: none

0x7D- 32-bit A8R8G8B8 Palette: none Compression: none

0x7F - 24-bit A0R8G8B8 Palette: none Compression: none

0x7E - 16-bit A1R5G5B5 Palette: none Compression: none

0x78 - 16-bit A0R5G6B5 Palette: none Compression: none

0x6D - 16-bit A4R4G4B4 Palette: none Compression: none

0x61 - DXT3 4x4 packed, alpha premultiplied, Palette: none Compression: 4x4 grid compressed, half-byte per pixel

0x60 - DXT1 4x4 packed, 1-bit alpha, Palette: none Compression: 4x4 grid compressed, half-byte per pixel

Palette codes:

0x22 - 24-bit DOS

0x24 - 24-bit

0x29 - 16-bit NFS5

0x2A - 32-bit

0x2D - 16-bit

Text codes:

0x6F - Standard Text file

0x69 - ETXT of arbitrary length with full entry header

0x70 - ETXT of 16 bytes or less including the header

0x7C - defined Pixel region Hotspot data for image.

This entry can also contain Binary data, however the identifier byte for different binary types anything that isn't already defined with a type so make sure to try and get all codes down correctly. Examples of binary data consist of Palette animations, binary links to outside files, or plain binary data.

Bitmaps can contain embedded mipmaps (pregenerated reduced size images). Each successive mipmap is assumed to be exactly 1/4 the size of the last (1/2 width and 1/2 height). The dimensions of the original bitmap must be a multiple of 2 raised to the power of the number of mipmaps (eg: 2 ^ 1 for one mipmap, 2 ^ 4 or 16 for four mipmaps).

Each mipmap is encoded using the same scheme as the original image and it's data block is appended directly following the previous mipmap or original image in descending order. (Exception: DXT encoded bitmaps must be at least 4x4 pixels, but a 2x2 pixel mipmap is supported under this scheme. It's format is unknown.)

Overview of DXT compression

Microsofts DirectX Texture Compression uses what they call a 4x4 encoding. Basically, an image must be a multiple of 4 in width and height, because 4x4 blocks of pixels are compressed at a time, similar to encoding used in AVI/MPEG files. Each 4x4 block contains 16 pixels, each pixel using either 24bits or 32bits before compression. All 16 pixels use 512 bits of storage before compression. After compression, that block of 16 pixels is reduced to 64 bits, for an 8:1 compression ratio. The nice thing about DXT compression is its hardware accelerated by nVidia and ATI GPU's all the way back to the GeForce2 and Raedon 8000 series, leaving the CPU free to simulate.

The compression itself works in the following way. First, all 16 pixels in the 4x4 block are checked, and unique colors stored in a vector (usually just an array of 16 unsigned ints). Once all the pixels in a block are checked, the two color extremes are found among all the unique colors. (This is something I had a hard time with in my own version, so I'm currently just using the method from FSHTool.) These two color extremes make up color1 and color2.

Once color1 and color2 are found, they are reduced from 32bit color to 16bit color (RGB 5:6:5), and stored in the first 32bits of the compressed 64bit chunk of data. The rest of the colors in the 4x4 block are interpolated between thse two colors. Each pixel is only represented by two bits of information, as follows:

bits color used for pixel

---

00 color1 01 color2 10 2/3 color1 + 1/3 color2 11 1/3 color1 + 2/3 color2

Here is the layout of a 64bit compressed block:

|----------------------------| | 16bit RGB (5:6:5) color1 | <- 2 bytes |----------------------------| | 16bit RGB (5:6:5) color2 | <- 2 bytes |----------------------------| | 00 | 01 | 01 | 11 | <- 1 byte, first 4 pixels |----------------------------| | 01 | 11 | 00 | 11 | <- 1 byte, second 4 pixels |----------------------------| | 00 | 01 | 01 | 01 | <- 1 byte, third 4 pixels |----------------------------| | 11 | 11 | 00 | 00 | <- 1 byte, fourth 4 pixels |----------------------------|

You can see the second part of the block is very basic. Its a simple bitmap of 2 bits each representing 1 of four possible color values. A 00 means use color1, 01 means use color2, 10 means use two-thirds of color1 mixed with one-third of color2, and 11 means use one-third of color1 mixed with two-thirds of color2. This is DXT1 compression, as no alpha information is saved. DXT3 compression uses the same technique, but also stores another 64bits of information for the alpha component of each pixel, in a similar block. So DXT3 compression achieves a 4:1 compression ratio with alpha information included, rather than the 8:1 compression ratio without.